The present invention relates to an image forming apparatus including: an image carrier unit integrally having a plurality of image carriers, which respectively carries an image; and a unit containing portion which removably contains the image carrier unit. The present invention also relates to a technique associated with the image forming apparatus.
Conventional laser color printers are generally provided with a plurality of photoreceptor drums for carrying images corresponding to the respective colors in one direction.
In addition, some conventional laser color printers are provided with a plurality of drive motors corresponding to the respective photoreceptor drums rotatably secured to the bodies of the printers, so that the driving force of each drive motor can be individually transmitted to each of the photoreceptor drums, and thus, can drive all of the photoreceptor drums stably with a sufficient driving force.
In such laser color printers, a drum gear for transmitting a driving force to a photoreceptor drum is connected to each of the photoreceptor drums, and a plurality of body gears which receive a driving force from the drive motors are engaged with the respective drum gears.
The drum gears and the body gears are formed in such a manner that the center of each circle works as the center of rotation. However, in a precise sense, the center of rotation slightly deviates from the center of the circles. Therefore, the displacement rate on the outer circumference of the gears at the time of rotation (the displacement amount on the outer circumference per unit time) is not constant.
When images, carried by respective the photoreceptor drums, are sequentially superposed on a sheet of paper conveyed in the above-described laser printer, the respective images are misaligned due to the dislocation of the center of gear rotation. A solution is required so as to inhibit misalignment of images carried by the photoreceptor drums.
For this purpose, in the above-described laser printer, a phase reference point is predetermined for the respective gears based on the dislocation of the rotational center, and the phase differences between the adjacent drum gears and between the adjacent body gears are set so as to be respectively constant.